A single in-line memory module (SIMM) presents a high density, low profile single in-line package for electronic components such as dynamic random access memory integrated circuit components. Each module comprises a plurality of integrated circuit components mounted on a circuit panel card having contact surfaces adjacent one edge. A plurality of these circuit panels, or daughtercards, can then be mounted on a circuit board mothercard.
Sockets known as SIMM sockets are well known to receive the edge of a circuit panel daughtercard and establish an electrical interconnection with a circuit board mothercard. U.S. Pat. No. 4,946,403 discloses a SIMM socket which permits a circuit panel to be inserted into the socket with a low insertion force. This patent also discloses a right angle SIMM socket for mounting the daughtercard parallel to the mothercard in order to reduce overall height of a packaged daughtercard/mothercard assembly. A problem with right angle mounting is that the mothercard must have a relatively large surface area to accommodate a plurality of daughtercards.
U.S. Pat. No. 5,041,005 discloses a low profile SIMM socket which permits mounting a daughtercard at an angle such as twenty-five degrees relative to the mothercard. This socket permits a plurality of daughtercards to be mounted in parallel side by side relationship while still providing a relatively low overall height for the packaged assembly.
In order to achieve a still denser array of daughtercards on a mothercard, it would be advantageous to narrow the SIMM sockets in order that they could be mounted on the mothercard in closer parallel relationship. Width of the sockets is primarily limited by the profile of the terminals which must be housed therein. Each of the above-referenced patents discloses a socket housing having a central rib which extends beneath a panel receiving slot along a length of the housing. The patents disclose terminals which are retained in their respective socket housings by two separate and spaced apart retention elements, one of the elements engaging on the central rib, and the other of the elements engaging an inner surface of an outer wall of the housing. Width of the sockets could be reduced if the terminal retention elements were localized so as to engage only one portion of the socket housing, in particular, the central rib.
Additionally, the above-referenced patents disclose camin sockets wherein a daughtercard is inserted into the socket at a first angle relative to the mothercard, the insertion being resisted by a zero or low insertion force. The daughtercard is then rotated to a second angle relative to the mothercard, the rotation being resisted by spring portions of the terminals which are designed to provide a relatively low resistance to the rotation. Each of the terminals has two contact portions for engaging opposite sides of the daughtercard. One of the contact portions is disposed on a substantially cantilever spring arm, and the other of the contact portions is disposed on a substantially C-shaped spring arm. Each of the spring arms must have a low spring rate in order to provide a fairly uniform normal force on different daughtercards having a thickness tolerance which varies over a relatively wide range. The C-shaped spring arm has multiple flexuous sections along its length and therefor has an inherently lower spring rate than the cantilever spring arm which has only one flexuous section at its root. It would be advantageous for the terminal to have contact portions on a pair of curved spring arms having low spring rates so that the socket would be more tolerant of variations in daughtercard thickness.
The present invention provides a SIMM socket having a reduced profile to enable denser packaging on a circuit board. The socket includes a housing having a central rib and terminals which are retained in the housing by opposed surfaces of the terminals gripping opposite sides of the central rib. The terminals have contacts disposed on substantially C-shaped spring members which have low spring rates so as to accept circuit panels having a wide range of thicknesses.